DTPA or EDTA?

Hello,

Plant fertilizers are available as liquid or substrate fertilizers. Both should only contain the micro nutrients. Liquid fertilizers have to be dosed more frequently; substrate fertilizers will last longer. Since there are no obvious differences in efficiency, it is up to the aquarists' preference which to use.
Next to the micro nutrients, fertilizers contain chelates. The chelate is an organic molecule which binds metal ions thus protecting them from early precipitation. The preferred type is abbreviated DTPA because of its stability up to a pH level of 7.5
Unfortunately some fertilizers contain the chelate EDTA, which is much cheaper. However chelate EDTA is only stable at a pH up to 6.0 and therefore mostly useless in aquariums.

What type of aquarium are you running? i.e. south american, african, etc. My Quantitative Chemical Analysis textbook shows that EDTA is capable of chelating metal ions at various pHs, depending on the major species of EDTA present (metal-EDTA complexes become less stable at lower pH ranges.)

Also, you can use any pH value to select which metal ions you want to be chelated by the EDTA and which ones will not be chelated. (example from my book: if a solution containing both Fe3+ and Ca2+ is titrated at pH 4, the Fe3+ is titrated (chelated by the EDTA) without any interference from Ca2+)

When you go to type in the "Quick Reply" box below my post, you can click on "Go Advanced" and it will bring you to another page. On this page, about halfway down, there is a button that says "Manage Attachments." From there, you can upload pictures straight from your computer.

You have to also include water hardness as ngrubich eluded to with his Ca+ example.

You won't be able to see a difference between DTPA and EDTA if you're dosing EI. Iron is a trace element so you don't need a lot and the difference(if there is one) between DTPA/EDTA will be masked by a lot of other variables that have greater effects on the plants (light, CO2, other traces, etc.).

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